Dear @Lin.Ding,
Increasing UACutOut should eliminate the warning. We added the functionality to disable UA at high angles of attack to improve numerical robustness of the solution for cases involving transients with large yaw angles arise (before the ability to temporarily turn off UA was added, OpenFAST would abort when the angle of attack reached UACutOut). I’m not sure how to test the validity of the UA model at higher angles of attack without other data to compare to (wind tunnel experiments or surface-resolved CFD of pitching airfoils for the airfoils of interest). I just know that the theory was developed for small to moderate angles of attack, and the 45-degree DEFAULT value of UACutOut is already quite high.
Best regards,